KR0148016B1 - Television tuner oscillator with three point tracking - Google Patents

Abstract

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Description

Oscillator with Adjusted Tuning Characteristics

1 is a block diagram of a television receiver tuner incorporating features of the present invention.

2 is a schematic diagram of a relevant part of the prior art oscillator of FIG.

3 is a schematic representation of the oscillator of FIG. 2 modified in accordance with the present invention.

* Explanation of symbols for main parts of the drawings

10: VHF tuning unit 12: signal source

14: varactor voltage control single tuning filter circuit

16: RF amplifier

18: varactor voltage control double tuning filter circuit

20: voltage controlled VHF local oscillator 22: mixer

307: varactor diode 311, 313: band switching diode

315,317: Bypass filter

FIELD OF THE INVENTION The present invention relates to a multi-band oscillator for use in television receivers and the like having an extended frequency range for three point tracking over multiple bands.

Voltage controlled tuners are widely used in television receivers. The tuner includes a local oscillator each having an RF input stage and each frequency selection circuit controlled in response to a tuning voltage. In response to the tuning voltage, the RF input selects one of a plurality of received RF carriers corresponding to the selected station and the local oscillator generates a local oscillator signal having a predetermined frequency associated with the selected channel. The selected RF carrier and local oscillator are heterodyne by mixing to produce an IF signal processed by an IF stage in the television receiver to generate an auditory and visual response.

The television range includes a plurality of separate frequency bands. The current US television signal spectrum for Ultra High Frequency (VHF) and Cable Television Network (CATV) channels (except for broadcast UHF channels of channels 14 to 83 between 470 MHz and 890 MHz) extends between 54 and 88 MHz and includes VHF channels 2 through 6. And a high / medium VHF band extending between 120 and 216 MHz and comprising CATV channels A to I and VHF channels 7 to 13, and three bands of CATV band extending between 216 and 300 MHz and including CATV channels J to W. Can be divided.

Typically, the frequency selection circuit is connected to or is connected to a plurality of tunable resonant circuits and at least one fixed inductor, each of which includes a voltage-controlled variable capacitance diode, commonly referred to as a varactor diode. It includes an inductor device formed in common with the inductor. Typically, the capacitance range of the varactor diode is not large enough so that the tuned circuit is tuned over the entire VHF range. As a result, it is common for the circuit tuned in the RF section and the local oscillator of the voltage controlled television tuner to include circuits each using a switching diode to select different inductor structures for each VHF and CATV band.

Typically, for a three-band tuner, a pair of band switching diodes operate to achieve different resonance states that tune each of three different bands in response to a suitable band switching signal that combines three different common inductors and varactor diodes.

One problem with a super heterodyne receiver is the maintenance of a constant frequency difference (same as the intermediate frequency) between a signal circuit such as an RF stage and a local oscillator circuit. For all tuning adjustments, the oscillator circuit should be arranged such that the difference between the resonant frequencies of the RF and oscillator tuning circuits is near the intermediate frequency. Since tuning of the local oscillator circuit is usually followed by tuning of the RF circuit, depending on whether the local oscillator is tuned below or above the signal frequency, the local oscillator has a larger or smaller percentage of frequency range relative to the center frequency than the RF circuit. Should be synchronized with By proper matching of the circuit components of the oscillator, it is possible to achieve close tracking at three frequencies within a specific band. If the above three frequencies where local oscillation tuning is correct are chosen close to the stage of the tuning range of the receiver for a particular band with a third frequency close to the arithmetic or geometrical meaning of the frequency band, the maximum value of deviation above or below the correct frequency should be It will be near or minimum. Thus, to achieve three-point tracking, it is necessary to adjust the frequency tuning curves for the varactor voltages to match the various circuits for the various bands with respect to the frequency change versus the change in the tuning voltage.

Since there is a threshold of conditions that must be set for oscillation, the tracking curve of change in frequency versus change in tuning voltage can be difficult to implement. The oscillator includes an amplifier having a frequency determining network and a feedback path between the output and the input of the amplifier configured to form a regenerative amplifying network (positive feedback) at a desired frequency determined by the frequency determining network. Typically, voltage controlled oscillators used in television receivers include a transistor amplifier and a frequency determination network comprising an inductor and varactor diodes in series or in parallel.

In practice, the individual elements of the oscillator are complex components comprising resistive, capacitive and inductive components. When the oscillation frequency is changed, the conditions for oscillation are disturbed, so that the relationship between the various components changes. For example, when the capacitance of a varactor diode increases with respect to the reduced tuning voltage applied across the diode's anode and cathode terminals, the response component of the diode at a particular frequency is reduced, such that the resistive component of the oscillator It binds more closely to other components and affects other components of the oscillator. This may be seen as a change in phase of the feedback signal causing a loss or possible duplex causing a reduction in the amplitude of the useful signal to be fed back between the amplifier output and input.

[Overview of invention]

Briefly, the invention relates to a device for varying the effective tuning inductance in response to a change in the frequency of a multi-band oscillator, wherein the frequency is controlled in response to the amplitude of the tuning voltage for the tuning signal amplifier, so that three-point tuning is such tuning. It can be made in the lowest frequency band of the oscillation period of the signal amplifier. In accordance with the present invention, a reactance network is coupled in series with the lowest band tuning inductor, which adjusts the tracking of the oscillator frequency as the tuning voltage changes.

Hereinafter, the present specification will be described in more detail with reference to the accompanying drawings.

Referring to the drawings in which the same reference numerals are applied to the same members, a typical tuning circuit for selectively tuning a television receiver, for example, to any channel within the VHF and CATV frequency bands, is shown in FIG. 1 in block diagram form. A VHF tuner, typically designated 10, receives an RF signal from a signal source 12, such as an antenna or cable network, and transmits the received RF television signal to a varactor voltage controlled single-tuned filter circuit. To The RF signal is then amplified by an RF amplifier 16 having the output of the amplifier 16 typically coupled via another varactor voltage controlled double tuned filter circuit 18. The varactor control filter circuits 14 and 18 select one channel from among the many channels received from the signal source 12.

The voltage controlled VHF local oscillator 20 is a tuned varactor and generates a local oscillator signal with a fixed frequency that is typically selected to be greater than the center frequency of the selected channel, thus, the difference (or sum) of the local oscillator signal and the frequency of the selected channel Will be the selected intermediate frequency (IF) of the system. The selected RF signal and local oscillator signal are applied to mixer 22 which is heterodyne to generate an IF signal. The IF signal is filtered and amplified by the IF unit 24 and then applied to an image and sound signal processing unit (not shown).

To tune the entire frequency, a single tuning filter circuit 14, a dual tuning filter circuit 18, and a local oscillator each comprise different tuning circuit structures for the low VHF band and the high VHF band and the CATV band. In particular, the tuned circuits each include varactor diodes that are originally connected in parallel with the different inductor structures selected in response to each one band select signal.

Referring to FIG. 2, a local oscillator circuit of the prior art is shown. The circuit of FIG. 2 is a schematic diagram of the relevant portion of the oscillator described in FIG. 1 of US Pat. No. 4,743,866, which is expressly incorporated herein by reference and is granted to Muterspaugh, a common assignee, as the present application. For the detailed operation of the circuit of FIG. 2, reference should be made to the relevant parts of the aforementioned patent, wherein each member shown in FIG. 2 is the same reference numeral as the corresponding member shown in FIG. 1 of the above-mentioned United States patent. Was granted.

Briefly, however, an amplifier circuit, typically designated 100, includes a double gate N-channel metal oxide semiconductor (MOS) field effect transistor (FFT) 101. A circuit 200 for controlling the oscillation of the amplifier 100 is coupled between the output of the source electrode S of the FET 101 and the input of the first gate electrode G1, and between the source electrode S and the signal ground. A capacitor 201 and a resistor 117 connected in parallel and a capacitor 203 coupled between the source electrode S and the first gate electrode G1 form a Colpitts-type oscillator.

Briefly, circuit 300 is a series tuning circuit that includes ductors 301, 303, and 305, and varactor diode 307 coupled in series with DC blocking capacitor 309. Band-switching diodes 311 and 313 and associated bypass filters 315 and 317 band-switch circuit points that exist in the middle of inductors 301 and 303 and circuit points that exist in the middle of inductors 303 and 305. Depending on the level of voltages BS1 and BS2, selectively bypass each to ground. Varactor diodes 307 and 209 are poled to tuning voltage VT to indicate that the capacitance of the diode changes in the same direction in response to a change in amplitude of the tuning voltage. Resistor 150 provides a DC feedback to the varactor, and capacitor 152 AC grounds the cathode of varactor diode 209.

In the lowest band 1, series inductors 301, 303 and 305 form the inductance of the resonant circuit. For three point tracking, it is necessary to adjust the tuning ratio of the change in oscillator versus tuning voltage of the low frequency single phase as previously described herein. The adjustment is difficult, but the difficulty is overcome by the network 400 of FIG. 3, in which the members are denoted by the same numbers corresponding to the same members of FIG.

As previously described herein, in order to better track the change in the tuning signal frequency of the RF signal filter determined by the commonly induced tuning voltage, the change in the oscillator frequency versus the tuning voltage applied to the oscillator is dependent upon the change. It is desirable to adjust the delivery characteristics of the oscillator. The network 400 of FIG. 3 does this. The inductor 301 of FIG. 2, which is 500 nHy in FIG. 3, is divided into two series configurations in which an inductor 301a of 200 nHy and an inductor 301b of 300 nHy are combined. An inductor 301b is coupled in parallel with a capacitor 301c of 47 picofarads pf.

In a typical embodiment, for band 1, the oscillator frequency will vary from 101 MHz for channel 2 to 129 MHz for channel 6. Inductor 301b and capacitor 310c of network 400 form a parallel resonant circuit R that resonates in parallel at 42 MHz. Therefore, at the oscillator frequency related to band 1, oscillation is performed at a frequency on the high frequency side of the resonant frequency of the oscillator resonant circuit R, and thus the resonant circuit R exhibits a capacitive circuit reactance. However, the total amount of capacitive reactance does not change linearly with frequency, but instead converts it according to a reactance curve commonly available for tuning circuits. Since the capacitive and inductive reactances are opposite signs of each other, the capacitive reactance of the parallel resonant circuit R, which is equal to or greater than the parallel resonant frequency of the parallel resonant circuit R, is a nonlinear method for the conversion of the oscillation frequency. Reduce some.

Thus, the frequency change of the oscillator for a given change in the tuning voltage applied to the oscillator is adjusted or changed as desired. In a typical embodiment, the response impedance of the network 400 shows an inductance of the inductive line 136 mHy at 101 MHz and 163 nHy inductance at 129 MHz instead of 173.7 nHy, which would be a linear increase in the inductive reactance of the 136 nHy inductor at 129 MHZ. In this way, the oscillation frequency of the oscillator may be adjusted for changes in the tuning voltage in a non-linear way to the change in the tuning voltage, just as a given change in tuning voltage changes less than normally changing the oscillator frequency. Can be.

In a typical embodiment, the network 400 is shown to include a parallel resonant circuit (R). A series resonant circuit can be used within the scope of the intention of the present invention. One such alternative embodiment (not shown) would be an inductor 301a that is 209nHy, an inductor 3016 (checked from the circuit) that is 0nHy, and a capacitor 301c that is 34pf. In such a structure, a nonlinear change in the inductive reactance of the network 400 with respect to frequency will have a different curved form that can be used if appropriate. However, in this alternative embodiment, if the remainder of the typical oscillator structure of FIG. 3 is maintained, measures should be made to provide a DC ground return for the band switching diodes 311 and 313.

Thus, the implementation of three point tracking for band 1 as previously described herein adjusts the propagation characteristics of the change of the oscillator frequency to the change of the oscillator frequency for all RF signal tuning circuit changes with commonly induced tuning voltages. Can be done.

Since the tuning reactance of the tuning reactor uses a circuit R tuned below the resonance point, it can actually be changed non-linearly with respect to frequency, in which case the response impedance of the tuning circuit can be induced whether the tuning circuit is parallel or resonant tuning. It will be your last name. Thus, the resonant circuit R resonated above the relevant oscillator band can be used below resonance to add an inductive reactance to the inductive reactance of the tuning inductance or to subtract the inductive reactance from the capacitive reactance of the tuning capacitor.

Although now considered and described to be preferred embodiments of the invention, it is understood that various changes and modifications may occur to those skilled in the art and that the appended claims fall within the true spirit and scope of the invention. It is intended to include all such variations and modifications as defined in the following.

Claims (2)

An oscillator having tuned tuning characteristics in a television receiver tuner comprising an amplifier and a feedback means for adjusting the amplifier to oscillate at a frequency determined by a tuning means comprising a reactive tuning element in response to the tuning voltage Wherein the tuning means comprises a resonant circuit (R) coupled to the reactive tuning element for adjusting a response to the tuning voltage, wherein the reactive tuning element is a first inductive element and the resonance circuit forms a network. And a second inductive element coupled in parallel with the capacitance element. 2. An oscillator with tuned tuning characteristics according to claim 1, wherein said network is coupled in series with said first inductive element.

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